Installed across the globe from 1943 to 1945, these fifty-five-ton phone scramblers would be used for D-Day, the Allied invasion of Germany, the bombing of Hiroshima, and the “dismemberment of the surrender instrument”—allowing Roosevelt, Truman, Churchill and Eisenhower to discuss the world’s fate with voices they barely recognized, voices not human but polite artificial replicas of speech rendered from digital pulses 20 milliseconds in length.

The SIGSALY Guam Terminal, codename NEPTUNE, with vocoder walls and turntables (left), photographed in 1945. Logistics concerning the atomic bomb missions and plans for the invasion of Japan were discussed over this secret radiotelephone link. (Courtesy National Archives/ NSAz/ Mahlon Doyle)